Lately, with remarkable downsizing and increase of performances of electrical devices such as personal computers, it is being strongly demanded to downsize and to save a space of a cooling mechanism for cooling exothermic parts such as MPUs mounted in the electrical devices. Because the MPUs are extremely integrated and carry out calculations, controls and others in high speed, they dissipate a large amount of heat. Then, various cooling systems have been proposed to cool chips and others, i.e., high-speed, high-output and highly integrated parts. Typical one of such cooling systems is a heat pipe.
Because apparent thermal conductivity of the heat pipe excels by about several times to several score times as compared to metals such as copper and aluminum, it is being adopted as a cooling element in various heat-related apparatuses.
The heat pipes include a round pipe-type heat pipe and a plane-type heat pipe in terms of their shapes. The plane-type heat pipe is preferably used for cooling parts to-be-cooled such as a CPU of the electronic devices because it may be readily attached to the parts to-be-cooled and it permits a large contact surface. Along with the downsizing and space-saving of the cooling mechanism, a heat pipe is required to be thinned in such cooling mechanism using the heat pipe.
The heat pipes may be also categorized, in terms of position where the part to-be-cooled is located, into those of a top heat mode in which the part to-be-cooled is located at an upper part and a bottom heat mode in which the part to-be-cooled is located at a lower part. While a fluid refluxes due to the gravity in the bottom heat mode, the fluid must be refluxed against the gravity and then a wick capillary phenomenon is generally utilized in the top heat mode.
The heat pipe is provided with spaces therein as working fluid flowing passages and the working fluid stored in the spaces moves heat by changing its phases such as evaporation and condensation and by moving within the pipe. Operations of the heat pipe in which heat is transported by the phase transformations and move of the working fluid stored in concealed hollow portions will be explained in detail below.
The heat pipe absorbs heat generated by the parts to-be-cooled and thermally conducted through a material of a container composing the heat pipe as latent heat on a heat-absorbing side thereof. Then the working fluid evaporates and its vapor moves to a heat-radiating side of the heat pipe. The vapor of the working fluid radiates the latent heat by condensing at the heat-radiating side and returns to a liquid-phase state. The working fluid thus returned to the liquid-phase state moves again (refluxes) to the heat-absorbing side. Heat is thus moved by the phase transformation and move of the working fluid. The working fluid returned to the liquid-phase state due to the phase transformation moves (refluxes) to the heat-absorbing side by the gravity in a gravity type heat pipe.
In a prior art thin heat pipe fabrication technology, a flattening process is carried out as an additional process after fabricating a heat pipe with combinations of a grooved pipe, of a bear pipe and meshes, of a bear pipe and braided wires, of a bear pipe and sintered metals, of a bear pipe and fine fiber wicks, and others (if a heat pipe is φ3 to φ6 for example, it is flattened around to 2.0 mm to 4.0 mm thick).